The present invention relates to a control apparatus for an internal combustion engine, and in particular to a control apparatus for an internal combustion engine, which can precisely control the volume of fuel or air in a fuel-priority type internal combustion engine wherein the flow rate of air is controlled by an electronic control valve.
These years, even in the technical field of automobiles, there has been demanded internal combustion engines of low fuel consumption type on the background of worldwide efforts for energy saving measures. As to internal combustion engines which can satisfy the above-mentioned demand, lean-burn type internal combustion engines have been most preferable. Among the lean-burn type internal combustion engines, a cylinder injection type internal combustion engine can, in particular, perform combustion with an air-fuel ratio higher than 40 by directly injecting fuel into an engine cylinder so as to stratify the mixture, thereby it is possible to aim at reducing pumping loss.
In comparison with control systems for conventional internal combustion engine, a control system for the above-mentioned lean-burn cylinder injection type internal combustion engine utilizes, in general, an electronic throttle for electronically controlling an air flow rate since no proportional relationship is present between the air flow rate and the torque of the engine.
Further, the control system for a lean-burn internal combustion engine requires torque demand control in order to obtain a toque the driver desires over a broad air-fuel ratio range. There has been two types of the torque demand, that is, an air priority type and a fuel priority type.
As to the air priority type, as shown in FIG. 14, a desired torque computing means and a desired air-fuel ratio computing means determine a desired torque and a desired air-fuel ratio, and a desired air-fuel volume computing means computes a desired air volume with which the desired torque and the desired air-fuel ratio can be obtained. Then, an electronic throttle controls the air-volume while an air volume sensor detects an actual air volume, and a fuel injection volume computing means determines a fuel injection volume from the actual air volume and the desired air-fuel ratio.
On the contrary, as to the fuel priority type, as shown in FIG. 15, a desired torque computing means determines a desired torque, and a fuel injection volume computing means determines a fuel injection volume with which the desired torque is obtained. Further, a desired air-volume computing means computes a desired air volume from the desired fuel injection volume and a desired air-fuel ratio, and then an electronic throttle controls the air volume. Further, with the fuel priority type, F/B control can be made for the air volume in accordance with an output value from an air-flow rate sensor.
By the way, as mentioned above, in the fuel priority type, a technique for computing a desired fuel volume with which a desired torque can be obtained, from an accelerator opening degree and a speed of the internal combustion engine, is in general used. Accordingly, it is required to previously determine the relationship between the accelerator opening degree and the desired fuel volume, depending upon a performance of the internal combustion engine.
Meanwhile, it is required to maintain the air-fuel ratio at a constant value in order to efficiently purify exhaust gas from an internal combustion, and accordingly it is required to set the maximum value of the fuel volume to a value corresponding to an air volume in an engine cylinder upon full opening of a throttle. Should a fuel volume greater than the value corresponding to an air volume in an engine cylinder upon full opening of the throttle be fed into the internal combustion engine, fuel would be excessive, resulting in deterioration of HC and CO.
However, the air-volume in the engine cylinder upon full opening of the throttle varies, depending upon the atmospheric pressure and the atmospheric temperature or EGR, opening and closing timing of intake and exhaust valves and the like. For example, when the atmospheric pressure lowers and the air volume in an engine cylinder decreases upon full opening of the throttle, fuel becomes excessive if a predetermined fuel volume as mentioned above is fed into the internal combustion engine upon full opening of accelerator, resulting in deterioration of exhaust gas.
On the contrary, if, for example, the opening and closing timing of the intake and exhaust valves varies so that the air volume in the engine cylinder upon full opening of the throttle increases, the throttle does not reach its full opening even though the accelerator is fully opened, and accordingly, a maximum torque cannot be obtained, thereby it is possible to raise such a problem that the performance of the internal combustion engine cannot be sufficiently used.
Further, the fuel volume fed into the internal combustion engine is in general divided mainly into a part for an internal loss and a part for a shaft torque. However, the internal loss is not uniform, but varies due to such causes as unevenness in mass production and aging effect. As mentioned above, the fuel volume to be fed is limited to the value corresponding to an air volume in an engine cylinder upon full opening of the throttle, and accordingly, there has been raised such a problem that since the internal loss varies, the shaft torque should be adjusted accordingly.
In view of the facts as mentioned above, the control for the fuel priority type internal combustion engine requires changing the maximum value of the fuel supply volume in accordance with an air volume in the engine cylinder upon full opening of the throttle, and further, requires changing the fuel volume for the shaft torque in view of a maximum value of the fuel supply volume and an internal loss. With the provision of these functions, it can be expected to enhance the exhaust performance and the operating performance.
As prior art of control for the fuel priority fuel injection type internal combustion engine, there has been proposed (Japanese Laid-Open H11-159317) a control device for controlling the throttle opening degree in order to compensate a delay of air from the throttle to the cylinder. Further, as to prior art of another control for the fuel priority cylinder injection type internal combustion engine, there has been proposed (Japanese Laid-Open Patent No. H11-159377) a control device for adjusting the fuel volume to a phase of an air volume in the cylinder is proposed.
However, any of those of the above-mentioned prior art concerns a control device for compensating a difference between the transmission characteristic of air from the throttle to the engine cylinder and the transmission characteristic of fuel, but does not concerns with a variation in air-volume in the engine cylinder and variation in internal loss upon full-opening of the throttle, that is, no consideration has been made for these variations.
The present invention is devised in view of the above-mentioned problems, and an object of the present invention is to provide a control apparatus for a fuel priority type internal combustion engine, which is highly robust against variation in various conditions so as to cope with variation in air volume in an engine cylinder, variation in internal loss and the like upon full opening of a throttle throughout the control of the fuel priority cylinder injection internal combustion.
To the end, according to the present invention, there is provided a control apparatus for a fuel priority type internal combustion, which basically computes a desired fuel volume, and then computes a desired air volume from this desired fuel volume and a desired air-fuel ratio, characterized by means for detecting an operating condition of the internal combustion engine, means for detecting an environmental condition surrounding the internal combustion engine, and a means for computing a desired fuel for the internal combustion engine in accordance with the operating condition of the internal combustion engine and the environmental condition surrounding the internal combustion engine (FIG. 1).
Further, in a configuration of the present invention, there is provided a control apparatus for an internal combustion engine which is of a fuel priority type, comprising means for detecting an operating condition of the internal combustion engine, means for detecting an environmental condition surrounding the internal combustion engine, a means for computing a desired fuel volume to be fed into the internal combustion engine, in accordance with the operating condition of the internal combustion engine and the environmental condition surrounding the internal combustion engine, and a means for computing a correction value of the desired fuel volume in accordance with the operating condition of the internal combustion engine and a condition surrounding the internal combustion engine (FIG. 2).
The control device for the internal combustion engine according to the present invention has such a function for computing a desired fuel volume by computing a correction value for the desired fuel volume in accordance with an operating condition of the internal combustion engine, including an accelerator opening degree, and a condition surrounding the internal combustion engine, including a variation in the atmospheric pressure, for changing a maximum value of a fuel supply volume in accordance with an air volume in an engine cylinder upon full opening of a throttle in the fuel priority type internal combustion engine, and for changing a fuel volume for a shaft torque in view of the maximum value of the fuel supply volume and an internal loss, thereby it is possible to obtain an exhaust performance and an operating performance which are robust against various conditions.
Further, in a specific configuration of the control apparatus for an internal combustion engine, the desired fuel volume computing means is adapted to compute a desired fuel injection volume at least from an accelerator opening degree and a speed of the internal combustion engine (FIG. 3).
Further, the means for detecting an environmental condition surrounding the internal combustion engine, is adapted to detect an atmospheric pressure or an atmospheric temperature (FIG. 4). With this arrangement, when the atmospheric pressure and the temperature vary, the maximum inflow air volume varies so that the fuel volume can be corrected accordingly. This correction system may be of a limiter type and a gain type.
Further, the means for detecting an operating condition of the internal combustion engine, includes a means for detecting an opening degree of an EGR valve, a means for detecting opening and closing timing of variable intake and exhaust valves, and a means for directly or indirectly detecting a charging efficiency of air volume in a cylinder of the internal combustion engine, such as a means for detecting an operating angle of a means for enhancing an air flow of intake air (swirl control valve SCV) (FIG. 5). With this arrangement, a charge efficiency in the cylinder is detected, and if the maximum charging efficiency is changed, the fuel volume is corrected accordingly. For example, when the EGR valve is operated, the maximum charging efficiency varies by a value corresponding to an EGR volume, and accordingly, the fuel injection volume is also corrected accordingly. This correction system is of a limiter type or a gain type.
Further, the means for detecting an operating condition of the internal combustion engine includes a means for directly or indirectly detecting a torque or a fuel volume with which the internal combustion engine can maintain a desired speed in its idle condition (FIG. 6). Since there is presented a shaft torque of the internal combustion engine which is given by subtracting an internal loss from an exhibited torque, if the toque for maintaining the idle speed varies, the maximum value of the shaft toque varies accordingly. Thus, the torque for maintaining the idle speed is detected so as to correct the fuel injection volume. This correction system is of a limiter type or a gain type.
Further, the means for detecting an operating condition of the internal combustion engine is a means for detecting an exhaust component from the internal combustion engine (FIG. 7). With this arrangement, Maximum Fuel Volume greater than Maximum Air Volume (@Atmospheric pressure is low), that is, a rich exhaust air-fuel ratio condition or, Maximum Fuel Volume less than Maximum Air Volume (@Atmospheric pressure is high), that is, a lean exhaust air-fuel ratio condition, is computed from an output delivered from an exhaust gas sensor such as an oxygen sensor or an A/F sensor in order to correct the fuel injection volume.
Further, the means for detecting an operating condition of the internal combustion engine includes at least an accelerator opening degree detecting means for detecting an opening degree of the accelerator, a throttle opening degree detecting means for detecting an opening degree of the throttle, and an air volume detecting means for directly or indirectly detecting an air volume flowing into the internal combustion engine (FIG. 8). With this arrangement, a condition, that is, Maximum Fuel Volume greater than Maximum Air Volume (@Atmospheric pressure is low) or Maximum Fuel Volume less than Maximum Air Volume (@Atmospheric pressure is high) is computed from an output delivered from, for example, the accelerator opening degree detecting sensor, a throttle opening degree detecting sensor or an air flow sensor in order to correct the fuel injection volume.
Further, the control apparatus for a fuel priority type internal combustion engine according to the present invention incorporates a desired air-fuel ratio computing device for computing a desired air-fuel ratio, and a desired air volume computing means for computing a desired air volume from the desired fuel volume and the desired air-fuel ratio, the desired fuel volume correction value computing means computing the desired fuel volume correction value when the absolute value of a difference between an actual air volume and the desired air volume is less than a predetermined value while the accelerator opening degree is greater than a predetermined value, and the throttle opening degree is less than a predetermined value (FIG. 9). With this arrangement, if the throttle opening degree does not yet reach its full opening degree even though the accelerator opening degree reaches its full opening degree, such a condition as Maximum Fuel Volume less than Maximum Air Volume is obtained, and accordingly, control can be made such that the maximum fuel volume can be increased up to the maximum air volume, thereby it is possible to enhance the exhibition of the maximum torque.
Further, the above-mentioned control apparatus for a fuel priority type internal combustion engine incorporates a desired air-fuel ratio computing device for computing a desired air-fuel ratio, and a desired air volume computing means for computing a desired air volume from the desired fuel volume and the desired air-fuel ratio, the desired fuel volume correction value computing means computing a desired fuel volume correction value when the desire air volume is greater than an actual air volume by a predetermined value while the accelerator opening degree is greater than a predetermined value, and the throttle opening degree is greater than a predetermined value (FIG. 10). With this arrangement, if the throttle opening degree reaches its full opening degree even though the accelerator opening degree does not yet reach its full opening degree, such a condition as Maximum Fuel Volume greater than Maximum Air Volume is obtained, and accordingly, control can be made such that the maximum volume is decreased up to the maximum air volume, thereby it is possible to prevent deterioration of exhaust gas caused by excessive fuel.
Further, the above-mentioned desired fuel volume correction means may be a means for computing a maximum value or a gain of the desired fuel volume in the relationship among the accelerator opening degree, the desired torque and the desired fuel volume (FIG. 11 and FIG. 12).
Further, the control apparatus for a fuel priority type internal combustion engine according to the present invention comprises means for detecting an operating condition of the internal combustion engine, means for detecting a condition surrounding the internal combustion engine, a charging efficiency control means for controlling the charging efficiency of an air volume in an engine cylinder, such as a supercharger, wherein the charging efficiency control means is controlled in accordance with an operating condition of the internal combustion engine and an environment surrounding the internal combustion engine (FIG. 13). With this arrangement, for example, if the atmospheric pressure becomes lower so that the maximum air volume becomes smaller, the maximum air volume can be increased by the supercharger or the like.
As mentioned above, the control apparatus according to the present invention has such a function that the maximum value of fuel supply volume is changed in accordance with an air volume in a cylinder of the fuel priority type internal combustion upon full opening of the throttle, and the fuel for the shaft torque is changed in consideration with a maximum value of the fuel supply volume and an internal loss, thereby it is possible to offer an exhaust performance and an operating condition which are robust against various conditions.